The Thief 3 Q&A on Computer and Video Games chats with ION Storm's Randy Smith about the upcoming installment in the stealthy Thief series. They discuss various aspects of gameplay, including how the use of the Unreal engine is influencing things:

One of the biggest differences for Thief 3 is that it uses state-of-the-art rendering technology. We've got fully volumetric shadows, which other companies are using now; but as early as two months ago the only companies we knew that were using this were us and id Software.

We try to use the rendering technology for gameplay all the time, so in a room, say, you might have an oven that's casting light. So the fact that any object casts a shadow from any light source means that the player has a lot more control over lighting in Thief 3.